Method and device for controlling an electrically actuated wear adjuster

ABSTRACT

A method and a device for controlling an electrically actuated wear adjuster of a brake application device for vehicles, in particular rail vehicles. Said method comprises the following steps: a) determination of an actual application stroke of brake linings against an allocated brake disc or brake drum during service braking, in accordance with at least one measured brake application path that is traversed by the brake linings and with a measured braking force value that is allocated to said brake application path; b) comparison of the actual application stroke with a desired brake application stroke or a desired application stroke tolerance range and if the actual application stroke deviates from said stroke or range: calculation of an adjustment path from said deviation; c) electronic control of the wear adjuster in accordance with the calculated adjustment path.

BACKGROUND AND SUMMARY OF THE DISCLOSURE

The invention relates to a method and a device for controlling anelectrically actuated wear adjusting device of a brake applicationsystem for vehicles, particularly rail vehicles.

European Patent Document EP 0 699 846 A2 describes a brake applicationsystem for rail vehicles, having a caliper-type brake linkage for a discbrake which has, as the screw drive between two brake linkage parts, amechanically actuated wear adjuster constructed as a thrust rod actuatoror as a brake rod actuator. The wear adjuster keeps the brake pad playconstant in the event of a wearing of the pad or the brake disc. Thistakes place by a change of length of the screw drive, in the case ofthrust rod actuators, an increasing actuator length causing a reductionof the brake pad play. The drive of the known screw drive takes placemechanically by a brake linkage with a thrust rod which, in the event ofan excess stroke of a brake actuator constructed as a pneumaticcylinder—piston driving gear, is operated by a rocker lever. Anemergency release of the brake, that is, an emergency-caused brakingforce reduction of the brake being affected by braking force, takesplace by the pneumatic brake actuator. For the auxiliary release of thebrake not affected by braking force for maintenance work, for example,for changing the brake pads, the threaded spindle is rotated manually.

The present method and system in one embodiment measured values for theapplication path, and the assigned braking force values are used as thestarting basis for the calculation of the actual application stroke andof the adjusting path that may be required.

The method according to another embodiment is based on a predetermineddesired application point in which the brake pad play should be equal tozero. This desired application point is approached and then the wearadjuster, if necessary, is actuated until a measured electric brakingforce signal is present for the first time and the actual applicationpoint has been reached. The covered path between the desired applicationpoint and the actual application point of the brake pads will thencorrespond to the adjusting path. The subsequent restoring of the brakeapplication system into the release position therefore starts out fromthe actual application point, so that the brake pad play caused by wearwill no longer exist for future application movements.

The wear adjuster of all of the embodiments, instead of beingmechanically actuated, is electrically actuated. Thus, the knownmechanical large-size actuating mechanism is eliminated, which resultsin a smaller size. In addition, a more precise adjusting of the brakepad play than previously can be achieved. This increases the dynamics ofthe brake application system.

In the first embodiment, the covered application path of the brake padsduring the service braking is directly or indirectly measured on a movedcomponent of the brake application system.

During a service braking taking place with a higher braking force, thebrake force value and the respectively assigned covered application pathof the brake pads may be measured several times successively. By meansof the supporting points obtained therefrom, an essentially linearbraking force—application path course can be shown, from which theactual application stroke is mathematically extrapolated. Braking at ahigher braking force in this case is a braking during which brakingforce values of approximately more than 3% to 20% of a maximallypossible braking force value occur.

In contrast, during a service braking which took place at a lowerbraking force, only the braking force value occurring once and theassigned covered application path of the brake pads are used fordetermining the actual application stroke. Braking at a lower brakingforce is a braking during which braking force values of approximatelyless than or equal to 3% to 20% of a maximally possible braking forcevalue occur. At lower braking force values, this method is more precisebecause no strictly linear braking force—application path relationshipis yet present from which the application point could be extrapolated.

The adjusting of the brake pad play may take place in the not-appliedcondition of the brake application system. A relatively low andcost-effective drive of the wear adjuster will then be sufficient forgenerating only the braking force required for producing a measurablebraking force signal.

The second embodiment is implemented at least during the upgrading orinitializing from a emergency-released or auxiliary release position ofthe brake application system together with a test run.

These and other aspects of the present disclosure will become apparentfrom the following detailed description of the disclosure, whenconsidered in conjunction with accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an electromechanical brakeapplication system with an electrically actuated wear adjuster accordingto the disclosure.

FIG. 2 is a longitudinal sectional view of the wear adjuster of FIG. 1in a position of the maximal length.

FIG. 3 is a view of the wear adjuster of FIG. 1 in a position of theminimal length.

FIG. 4 is a program flow chart of a wear adjusting operation by the wearadjuster of FIG. 2.

FIG. 5 is a view of a typical characteristic braking force—applicationpath curve of the brake adjuster of FIG. 1.

FIG. 6 is a brake pad play—time diagram.

FIG. 7 is a program flow chart of a test run program for the brakeapplication system of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

An electromechanical brake application system, which, as a whole, hasthe reference number 1 in FIG. 1, forms one of several brake applicationsystems of a rail vehicle. The brake application device 1 contains abrake actuator 2 with a service brake unit and an accumulator-type brakeunit. The service brake unit has an electric drive, such as an electricservo motor 4, which is accommodated in an actuator housing 6 of thebrake actuator 2. A mechanical force converter 8 is used for convertingthe energy supplied by the brake actuator 2 to a brake applicationmovement.

The servo motor 4 causes a coaxial brake spindle 10 to rotate, whichrotations are converted by the force converter 8 to a brake applicationmovement of brake pads 12 in the direction of an axle-mounted brake disc14, which may also be a brake drum. The force converter 8 comprises,among other components, a nut/spindle constructional unit 16 with aspindle nut 18 which is rotatably disposed on the brake spindle 10 andwhich, when the brake spindle 10 is rotated, can carry out linearmovements in the direction of the spindle axis 42. The end of the brakespindle 10 facing away from the servo motor 4 projects into acylindrical hollow section of a connecting rod 20 which is non-rotatablyand axially fixedly connected with the spindle nut 18. In addition, thecylindrical hollow section of the connecting rod 20 is non-rotatably andaxially fixedly held in a sliding sleeve 22, which is acted upon by atleast one accumulator-type spring 24 supported on the actuator housing6. The accumulator-type spring 24 is part of the accumulator-type brakeunit and is used as an energy accumulator for storing and releasingenergy for the application of the brake as a service-type emergencybrake in the sense of an underlying safety level in the event of afailure of the service brake unit and/or as a parking brake. The servicebrake unit as well as the accumulator-type brake unit act upon theconnecting rod 20. In the brake release position, the accumulator-typespring is held in a preloaded position by means of a locking device 26.

The small end 28 of the connecting rod 20 projects out of the slidingsleeve 22 and is linked to a brake lever 36 by a hinge 40 perpendicularto the spindle axis 42. When the brake spindle 10 is driven in the brakeapplication direction or when the locking device 26 of theaccumulator-type spring 24 is released, because of the then axiallymoving-out connecting rod 20, a hinge pin of the hinge 40 is, amongothers, stressed by shearing forces acting essentially perpendicular tothe pin axis.

The other end of the brake lever 36 acts upon an eccentric arrangementhaving an eccentric shaft 46 which is hinged to a caliper lever 48which, together with another caliper lever 50, forms a caliper 52. Atone set of ends of the caliper levers 48, 50, respective brake padholders 54 are arranged which have brake pads 12 which are displaceablein the direction of the axis of the axle-mounted brake disc 14. The endsof the caliper levers 48, 50 facing away from the brake pads 12 areconnected with one another by a thrust rod actuator 156 which preferablyis designed to be electrically actuated. The described arrangement alsoforms a part of the force converter 8 which converts the moving-outmovements of the connecting rod 20 caused by the servo motor 4 or by theaccumulator-type spring 24 to a brake application movement of the brakepads 12 in the direction of the brake disc 14.

The hinge pin of the hinge 40 may be a shearing force measuring screw58. The shearing force measuring screw 58 is equipped with at least onetransducer, which is not shown for reasons of scale, for the measuringof quantities from which the braking force acting upon the brake pads 12can be indirectly or directly derived. The transducer may be straingauges (DMS) which are fastened to the circumference of the shearingforce measuring screw 58, for example, by gluing. They generate signalsproportional to the shear deformations of the shearing force measuringscrew 58 caused by the shearing forces acting in opposite directions.

Instead of being arranged on the shearing force measuring screw 58 or inaddition thereto, one or more strain gauges can also be arranged on thebrake lever 36 in order to be able to derive the braking forces from thedeformations of the brake lever 36.

A conversion of the shear deformation signals to signals for the actualapplication force acting in each case upon the brake pads 12 takes placein an electronic analyzing system containing a strain gauge bridgecircuit. These signals are transmitted by a signal line 59 to a centralcontrol and automatic control unit 60. A deviation between a desiredapplication force and the actual application force is computed there bymeans of a variance comparison. The desired-value definition for thebraking force depends, for example, on the reaching of a demandeddesired application force in a time period which is as short aspossible.

The control and automatic control device 60 controls a power part 62which, as a function of the computed deviation, modulates an operatingcurrent for the servo motor 4. The operating current is measured by acurrent sensor 66 connected to an electric line 64 extending between thepower part 62 and the servo motor 4. A corresponding motor currentsignal is fed back by a signal line 68 to the control and automaticcontrol device 60. In addition to being used for controlling a desiredapplication force, the signals for the actual application forcescontrolled into the control and automatic control device 60 are used asa basis for controlling the thrust rod actuator 156 by an electric line74. This control will be described later. The signals for the respectivemotor current are used for monitoring the force adjustment and of theoperability of the brake application system 1 during safety-relevantbraking. For verifying the measuring results, the motor current measuredon the drive side by the current sensor 66 can also be adjusted in thecontrol and automatic control device 60 to the signal for the actualapplication force.

An angle position encoder 70 arranged at the end of the motor shaft ofthe servo motor 4 facing away from the brake spindle 10 is used for theindirect measurement of the application path of the brake pads 12 duringan actuation of the brake actuator 2. A signal line 72, supplies acorresponding signal to the central control and automatic control device60 which converts the angle of rotation of the servo motor 4 to thecorresponding application path. As an alternative, any type of measuringsystem could be provided by which the application path of the brake pads12 can be directly or indirectly measured, for example, an absoluteposition measuring system. A limit switch 76 detects and reports therelease position of the brake actuator 2 to the central control andautomatic control device 60.

The brake application system 1 generates load-corrected and/orslip-controlled braking forces. A load-corrected braking force is abraking force essentially adapted to the respective present weight ofthe rail vehicle. A slip-controlled braking force is a braking force bywhich the braking takes place with an ideal wheel slip (anti-skidprotection control). For this purpose the control and automatic controldevice 60 has corresponding control operations. Furthermore, the centralcontrol and automatic control device 60 has electronic modules forcontrolling the thrust rod actuator 156 which in FIG. 1 is illustratedonly in a top view. The thrust rod actuator 156 is used for the wearadjustment for compensating the wear of the brake pads 12 and of thebrake disc 14 occurring during the operation. Instead of a thrust rodactuator 156, a brake rod actuator with a correspondingly adapted powerconverter 8 may be provided.

In the view illustrated in FIG. 2, the thrust rod actuator 156 isillustrated in a position of the maximal length. The adjusting path ismaximal because a lengthening of the thrust rod actuator 156 by thelinking of the caliper levers 48, 50 results in a reduction of thedistance of the brake pads 12 from the brake disc 14 and vice-versa.

The thrust rod actuator 156 contains a screw drive 2′ which, as thescrew parts, has a threaded spindle 4′ and a nut 8′ which can be screwedonto this threaded spindle 4′ by a trapezoidal thread 6′ and isconstructed as a tube-type part. The trapezoidal thread 6′ is notself-locking. For the wear adjustment, the thrust rod actuator 156 isdesigned to be electrically actuated. An electric drive unit 10′consists of an electric motor 12′ with a gearing 14′ connected behindit, whose gearing output is rotationally coupled with the spindle 4′. Asan alternative, the nut 8′ or the spindle 4′ and the nut 8′ can also bedesigned to be electrically actuated for adjusting the wear.

The electric motor may be a d.c. motor 12′. The gearing 14′ may be aplanetary gearing 16′ axially adjoining the d.c. motor 12′ as well as bya gearwheel stage 18′ connected to the output side of the planetarygearing 16′. The d.c. motor 12′, the planetary gearing 16′ and the gearwheel stage 18′ are arranged parallel to and at a radial distance fromthe center axis 20′ of the screw drive 2′. They are housed in a drivehousing 22′ flanged to a housing part 24′, shown on the left in FIG. 1,of the thrust rod actuator 156, to which thrust rod actuator 156 a leftcaliper lever 50 of the caliper 52 (FIG. 1) is linked. A right housingpart 26′, as viewed in the axial direction of the screw drive 2′, isopposite the left housing part 24′. The right caliper lever 48 of thecaliper 52 (FIG. 1) is linked to this right housing part 26′. Thespacing of the left housing part 24′ and the right housing part 26′ ofthe thrust rod actuator 156 is varied by the screw drive 2′ in that, byextending the screw drive 2′ or the thrust rod actuator 156, a wearadjustment can take place and the pad play between the brake pads 12 andthe brake disc 14, which increases with time, can be reduced again andcan be held at a constant value.

The gearing-output-side gearwheel 28′ of the gearwheel stage 18′ mesheswith a screw-side gearwheel 30′. Gearwheel 28′ is coaxially rotatablydisposed on a cylindrical projection 34′ of a conical sleeve 36′ by adeep-groove ball bearing 32′. A slip clutch 38′ arranged on the side ofthe spindle-side gearwheel 30′ pointing to the right housing part 26′couples the electric drive unit 10′ with the conical sleeve 36′. Theslip clutch 38′ contains balls 40′, which are pretensioned by a definedspring pressure in grooves constructed on the face of the spindle-sidegearwheel 30′ and which are guided in bores 42′ of a ring 44′non-rotatably held on the cylindrical projection 34′ of the conicalsleeve 36′. At torques greater than a defined slipping moment, the formclosure generated by the balls 40′ pressed into the grooves is overcomeand the clutch 38′ slips, whereby the electric drive unit 10′ isuncoupled from the spindle 4′. By the appropriate selection of thespring parameters and of the ball—groove geometry, the slipping momentcan be adapted to the momentarily existing requirements. In the presentcase, the clutch 38′ slips when the brake application system reachesstop positions, such as the position in which the brake pads 12 come torest on the brake disc 14 or the position in which the thrust rodactuator 156 is shortened to the minimal length (FIG. 3) and the spindle4′ is completely screwed into the nut 8′.

The driving torque transmitted by the slip clutch 38′ to the ring 44′ isintroduced into the conical sleeve 36′. A pin-shaped projection 46′ onthe end of conical sleeve 36′ has a radially outer surface, which formsa bearing surface of a slide bearing 48′. The bearing surface isslidably and rotatably disposed in a housing-side bearing surfaceassigned to it. The slip bearing 48′ is used as a bearing point of thespindle 4′, which bearing point is on the left side in FIG. 2. Thespindle 4′, in turn, is screwed by an end-side threaded pin 50′ into aninternal thread existing in the projection 46′ of the conical sleeve 36′and is held there in a non-rotatable manner. As a result, the conicalsleeve 36′ can transmit the driving torque introduced by the slip clutch38′ to the spindle 4′.

A cone clutch 52′ contains at least two conical surfaces 56′, 58′, whichcan be stopped by mutual friction against one another and are arrangedin an oblique manner viewed in the axial direction. The cone clutch 52′is arranged in front of the electric drive unit 10′, one of the conicalsurfaces 56′ being constructed on the left housing part 24′ and theother conical surface 58′ being constructed on the conical sleeve 36′screwed to the spindle 4′. When the spindle 4′ is axially loaded, thetwo conical surfaces 56′, 58′ are pressed against one another in thedirection of the conical narrowing. Whereby, the respectively taken-uprotating position of the spindle 4′ is fixed by frictional engagement oradherence and the axial load is supported by the left housing part 24′.In particular, a transmission of the axial load as a torque to theelectric drive unit 10′ is prevented. If, in contrast, no axial load ispresent, the cone clutch 52′ is in the released state and the conicalsleeve 36′, together with the spindle 4′, can rotate freely with respectto the left housing part 24′.

The tube-type nut 8′ projects into a stepped passage opening 60′ of theright housing part 26′ and is rotatably disposed there by a deep-grooveball bearing 62′ but is axially displaceably disposed with respect toits inner race. A sleeve 66′ is non-rotatably and axially fixedly heldin the end of the nut 8′ which points away from the left housing part24′. An outer circumference of sleeve 66′ rests slidingly on a seal 64′received in the passage opening 60′ of the right housing part 26′. Theend of the sleeve 66′ projecting out of the passage opening 60′ isequipped with an application surface 68′ for a screwing tool. A slipclutch 70′ couples the nut 8′ with a coaxial free-wheel sleeve 72′ of alockable free wheel 74′. The lockable free wheel 74′ is axiallydisplaceably held on the nut 8′ and is supported by a thrust bearing 76′that may be constructed as an axial needle bearing against a radial wall78′ of the right housing part 26′. The nut 8′ is therefore disposed in athrust-bearing type manner.

The slip clutch 70′ may be two side face gearings 80′, 82′ meshing withone another in the axial direction as a result of spring pressure. Oneside face gearing 80′ is constructed on a radially outer ring collar ofthe end of the nut 8′ projecting into the right housing part 26′, andthe other side face gearing 82′ is constructed on the radially innercircumferential surface of the free-wheel sleeve 72′.

A coil spring 86′ is supported at one end on the deep-groove ballbearing 62′ and at the other end on an outer step 84′ of the nut 8′. Thenut 8′ is pretensioned by the coil spring 86′ against the free-wheelsleeve 72′, so that the two side face gearings 80′, 82′ are in a mutualengagement. When a slipping moment is exceeded, the two contrategearings 80′, 82′ are disengaged while the nut 8′ is axially displacedin the direction of the left housing part 24′, whereby the nut 8′ canrotate with respect to the free-wheel sleeve 72′. The slipping moment ofthe slip clutch 70′ can be adapted by the suitable selection of thespring parameters and of the side face gearings 80′, 82′.

In the right housing part 26′, an electric drive unit 112′ isaccommodated for the emergency release and the auxiliary release of thebrake application system. “Emergency release” is a braking forcereduction of the brake application system 1 acted upon by braking force,for example, in the event of a failure of the brake actuator 2, and“auxiliary release” is a release of the brake not acted upon by brakingforce for maintenance work, for example, for changing the brake pads.

The electric drive unit 112′ consists of an electric motor, for example,a d.c. motor 114′, of a planetary gearing 116′ as well as of a gearwheelstage 118′, so that the two electric drive units 10′, 112′ may have anidentical construction. The gearing-output-side gearwheel 120′ of thegearwheel stage 118′ meshes with a toothed sleeve 96′ which is coaxialwith the screw drive 2′. The toothed sleeve 96′ is rotatablyaccommodated in the right housing part 26′ and is radially spaced by anannulus 102′ with respect to a housing surface 100′ which is flush withthe radially outer circumferential surface 98′ of the free-wheel sleeve72′ and axially adjoins the circumferential surface 98′ of thefree-wheel sleeve 72′. A coil spring 104′ which is coaxial with respectto the center axis 20′ of the screw drive 2′ and has two pin-type ends106′, 108′ bent away oppositely in the radial direction is accommodatedin the annulus 102′. One end 106′ is form-lockingly held in a radialpassage bore of the toothed sleeve 96′, and the other end 108′ isform-lockingly held in a radial passage bore of the free-wheel sleeve72′.

The toothed sleeve 96′, the coil spring 104′, the free-wheel sleeve 72′and the housing surface 100′ together form a lockable free wheel as acoil spring free wheel 74′, which couples the electric drive unit 112′with the nut 8′. More precisely, the coil spring free wheel 74′ rotatesthe nut 8′ by the electric drive unit 112′ in a direction against thewear adjustment and locks this rotation when the rotation of the nut 8′is not caused by the electric drive unit 112′. The above-described slipclutch 70′ is arranged between the nut 8′ and the coil spring free wheel74′.

Relative to an imagined point of intersection of the center axis 20′ ofthe screw drive 2′ and an imagined vertical center line of the thrustrod actuator 156, the two electric drive units 10′, 112′ are arrangedessentially point-symmetrically with respect to one another. Also, theypoint toward one another starting from the end of the spindle 4′ or ofthe nut 8′. More precisely, the drive unit 10′ for the wear adjustmentprojects essentially from the drive-side end of the spindle 4′ in thedirection of the drive unit 112′ for the emergency and auxiliaryrelease, and the drive unit 112′ projects essentially from thedrive-side end of the nut 8′ in the direction of the drive unit 10′ forthe wear adjustment. Both drive units 10′, 112′ actuate a single screwdrive 2′ for the combined wear adjustment and emergency or auxiliaryrelease.

The right and the left housing part 24′, 26′ each consists of housingsections 122′, 124′ which are essentially symmetrical relative to thecenter axis 20′ of the screw drive 2′. The drive units 10′, 112′ areeach accommodated in a separate housing section 122′. A final positionsensor 126′ is accommodated in the housing section 124′ arranged on theopposite sides of the center axis 20. The final position sensor 126 issituated opposite a face-side surface 128′ of the drive housing 22′ ofthe respectively other electric drive unit 10′, 112′. The final positionsensors may be mechanical final position switches 126′. They are eachactuated by engaging the face-side surface 128′ of the drive housing 22′of the opposite drive unit 10′, 112′. The actuation switches 126′ supplya signal to the central control and automatic control unit 60 (FIG. 1)when reaching the position illustrated in FIG. 3, in which the thrustrod actuator 156 has moved to the minimal length. Whereupon, therespectively actuated drive unit 10′, 112′ is de-energized. At theirends pointing away from one another, the two housing sections 122′, 124′of each housing part 24′, 26′ are in each case provided with onereceiving device 132′ for bolts, by which one caliper lever 48, 50respectively of the caliper 52 is linked to each housing part 24′, 26′.

Furthermore, a coil spring 138′ of another coil spring free wheel 140′is arranged on a cylindrical projection 134′ of theplanetary-gearing-side gearwheel 136′ of the gearwheel stage 18′assigned to the drive unit 10′ for the wear adjustment. This coil springfree wheel 140′ blocks a rotation of the gearwheel 136′ in the directionagainst the wear adjustment and permits it to run freely in the oppositerotating direction.

As a result of the described construction of the thrust rod actuator156, and specifically a single screw drive 2′, with one screw partrespectively is coupled with a separate drive unit; the brake pad wearcan be corrected, and the brake can be released for emergencies and/orin an auxiliary manner. Specifically, the spindle 4′ is coupled with oneelectric drive unit 10′, and the nut 8′ is coupled with the otherelectric drive unit 112′.

Based on this background, the method of operation of the thrust rodactuator 156 is as follows:

The wear adjustment, that is, the reduction of the brake pad play, whichexists between the brake pads 12 and the brake disc 14 and which hasbecome too large as a result of wear, preferably takes place in thebrake-force-free brake release position. For this purpose, the d.c.motor 12′ of the electric drive unit 10′ provided for the wearadjustment is controlled for a predetermined time and causes the spindle4′ to rotate in one rotating direction by the slip clutch 38′ closed inthe case of a driving torque which is smaller than the slipping moment.During the rotating movement, the spindle 4′ is screwed out of the nut8′ and the thrust rod actuator 156 is thereby lengthened, which resultsin a reduction of the brake pad play. FIG. 2 shows the thrust rodactuator 156 in a position of its maximal length. Since the screw drive2′ is thereby loaded by only very low axial forces, the cone clutch 52′is in the released position, so that the spindle 4′ can rotate freely.The nut-side coil spring free wheel 74′ blocks a rotating-along of thenut 8′, which is not secured against a rotation per se, because arotation of the nut 8′ is transmitted by the slip clutch 70′ to thefree-wheel sleeve 72′ and from there to the coil spring 104′ which thenpulls tight and establishes a frictionally engaged connection betweenthe free-wheel sleeve 72′ and the housing surface 100′. Thus the nut 8′is non-rotatably supported on the right housing part 26′.

During a braking, the bearing pressure force resulting from the brakingforce existing at the brake pads and transmitted by the hinged caliperlevers 48, 50 of the caliper 52 to the thrust rod actuator 156 andacting there in the axial direction could not be supported on the screwdrive 2′ because the trapezoidal thread 6′ between the spindle 4′ andthe nut 8′ does not have a self-locking construction. As a result, thethrust rod actuator 156 would be shortened under the influence of theaxial pressure force and causes an undesirable loss of braking force.However, the cone clutch 52′ closes under the effect of the axial loadby the pressing-together of the mutually assigned conical surfaces 56′,58′ in a frictionally engaged manner and establishes a non-rotatableconnection between the spindle 4′ and the left housing part 24′. On theother hand, the nut-side slip clutch 70′ constructed as a side facegearing 80′, 82′ remains closed under the axial load and transmits themoment of reaction to the coil spring 104′ which then pulls tight andsupports the moment of reaction at the right housing part 26′. As aresult, there is no shortening of the thrust rod actuator 156 and thusno unintended loss of braking force can occur during a brakingoperation.

If a fault occurs, in the case of a brake actuator 2 illustrated in FIG.1 or in its control, which has the result that the brake actuator can nolonger release the brake acted upon by the braking force, this brake hasto be subjected to an emergency release. For the emergency release ofthe brake, the electric drive unit 112′ is preferably controlled for theemergency and/or auxiliary release from an engineer's cab of the urbanrailroad or subway by the control and automatic control unit.Specifically, coil spring 104′ rotates in a direction in which the coilspring 104′ expands. As a result, the previously existing frictionalengagement between the free-wheel sleeve 72′ and the housing surface100′ is eliminated. Thus the nut 8′ has a free run in this rotatingdirection. The coil spring 104′ can therefore transmit the rotatingmovement introduced into it by the toothed sleeve 96′ to the free-wheelsleeve 72′. This rotation is transmitted to the now freely running nut8′ by the slip clutch 70′ which is closed because it is not overloaded.As a result, the thrust rod actuator 156 is shortened and the brakingforce is reduced. The thrust rod actuator 156 can thereby be shortenedto the minimal length illustrated in FIG. 3 in which the nut 8′ on theface side comes in contact with the bottom of the conical sleeve 36′ andthe final position switches 126′ are actuated, a corresponding signalbeing transmitted to the central control and automatic control unit 60.

If, for maintenance work, the brake is to be moved into a position inwhich the brake pads 12 are at a maximal distance from the brake disc,for example, for exchanging the brake pads 12, the auxiliary release ofthe brake can also take place by the electric drive unit 112′ for theemergency release in the manner described above. The torque is limitedwhich can be transmitted by means of the nut-side wrap spring 104′expanded by the driving torque and is subjected to a bending stress, inthe cases in which the screw drive 2′ is stiff, for example, because oficing. In this case, the nut 8′ is rotated directly for shortening thethrust rod actuator 156. This takes place in the braking-force-freestate by applying a screwing tool to the application surface 68′ of thesleeve 66′ non-rotatably connected with the nut 8′. The nut 8′ ismanually rotated in a direction in which the thrust rod actuator 156 isshortened to the minimal length illustrated in FIG. 3. The torque mustbe so large that the slip clutch 70′ arranged between the free-wheelsleeve 72′ and the nut 8′ can slip, while the coil spring 104′ of thecoil spring free wheel 74′ blocks the free-wheel sleeve 72′ in thisdirection. In this case, the nut 8′ is displaced sufficiently away fromthe free-wheel sleeve 72′ in the axial direction that the two side facegearings 80, 82 are disengaged.

In order to adjust a desired brake pad play between the brake pads 12and the brake disc 14 within the scope of the above-described wearadjusting, the thrust rod actuator 156 is controlled as follows by thecentral control and automatic control unit 60 according to the programflow chart illustrated in FIG. 4:

First, by the presence or absence of signals of the limit switches 126′,it is determined whether the brake application system 1 is in anemergency-released position or in a position released in an auxiliarymanner, which is illustrated in FIG. 4 by the branching “released in anauxiliary manner?”. If it is released in an auxiliary manner, theprogram is stopped. If it is not, the query “brake released?” takesplace because the wear adjustment preferably is to take place only inthe released position or in the not-applied condition of the brake. Whenthe brake is released, in which case the limit switch 76 generates acorresponding signal, the program is continued with the next programstep. A not-released brake therefore causes a return to the programstart.

Previously, the actual application stroke of the brake pads 12 to thebrake disc 14 during a preceding service braking was determined in thatthe application path traveled by the brake pads 12 and a braking forcevalue assigned to this application path was measured. The angle encoder70, which measures the rotating angle of the servo motor 4 during theservice braking and provides a corresponding signal to the control andautomatic control device 60, is used for measuring the application path.For example, in the present arrangement, 1 mm of application pathcorresponds to approximately 6 mm of spindle path or 3 revolutions ofthe servo motor 4. The control and automatic control unit 60 alsoreceives the force signal assigned to the measured application path fromthe shearing-force measuring screw 58 provided with a strain gauge. Fromthe two measured values—the application path and the braking force valueassigned to the latter—preferably as a function of the amount of thebraking force value, the actual application stroke is computed asfollows:

During a service braking taking place at a higher braking force, thebraking force value and the respectively assigned covered applicationpath of the brake pads 12 are measured several times successively inorder to provide supporting points from which the control and automaticcontrol unit 60 computes a theoretical linear characteristic brakingforce—application path curve which is illustrated in FIG. 5 as astraight line indicated by interrupted lines. The actual courseindicated by a solid line in FIG. 5 is congruent for higher brakingforces with the theoretical straight line. In this case, braking at ahigher braking force is braking during which braking force values occurof preferably approximately more than 3% to 20% of a maximally possiblebraking force value. By means of extrapolation, the theoretical andlinear characteristic braking force—application path curve is continuedto very small braking force values to a computed point of intersectionwith the abscissa which corresponds to the application point of thebrake pads 12 on the brake disc 14. This application point ischaracterized in that, after the contact stroke of the brake pads 12onto the brake disc 14 has taken place, a braking force value can bedetected for the first time by the shearing-force measuring screw 58.The actual application stroke of the brake pads 12 is then obtained fromthe abscissa value of this application point by the correspondingcomputation by the control and automatic control device 60.

As illustrated in FIG. 5, the course of the actual characteristicbraking force—application path curve is not linear at low brakingforces, so that, in this range, an extrapolation with sufficientprecision is difficult. Braking at a low braking force is a brakingduring which braking force values occur of approximately less than orequal to 3% to 20% of a maximally possible braking force value. Duringsuch a braking, preferably only the braking force value occurring forthe first time and the assigned covered application path of the brakepads are used for determining the actual application stroke. This meansthat, when the shearing-force measuring screw 58 as the braking forcesensor responds for the first time, the application path covered so faris stored and a calculation of the actual application stroke takes placetherefrom.

The control and automatic control unit 60 compares the determined actualapplication stroke with a defined desired application stroke or adesired application stroke tolerance range, which is illustrated in FIG.4 by the branching “application stroke too large or too small?”. If theactual application stroke deviates from the desired application strokeor from the desired-application-stroke tolerance range, the requiredadjusting path is calculated from the difference of these values, and ifnot, the program returns to the program start. Subsequently, the driveunit 10′ is controlled for the wear adjustment of the thrust rodactuator 156 as a function of the calculated adjusting path. This cantake place, for example, in that the drive unit 10′ is actuated for atime which depends on the calculated adjusting path, which in FIG. 4 isindicated by the “set timer” operation. The time—adjusting pathrelationship is known from the quantities rotational speed of the d.c.motor 12′ and the transmission ratio of the gearing 14′ stored in amemory of the control and automatic control unit 60. If the actuatingtime assigned to the required adjusting path has expired, which isqueried by the branching “has timer run out?”, the drive unit 10′ isdeactivated and the program returns to the start.

According to an alternative approach, the brake application system 1 isfirst actuated by energizing the actuator motor 4 until the brake pads12 have reached a position which corresponds to a defined desiredapplication point. When wear is present, this desired application pointof the brake pads 12 deviates from the actual application point, whenthe brake pads moved into the desired application point still have aclear distance from the brake disc 14 which corresponds precisely to thewear to be adjusted. Subsequently, the drive unit 10′ is activated forthe wear adjustment until the shearing force measuring screw 58 detectsa braking force signal for the first time, whereby precisely the wearpath is compensated. Finally, the brake actuator 2 is restored into therelease position.

The permissible brake pad play or the permissible wear can be permittedwithin a certain tolerance, as illustrated by FIG. 6, which shows thetolerance range between a maximally permissible brake pad play and aminimally permissible brake pad play by shaded lines. Adjustingoperations therefore will only take place in the event that the actualwear or the actual brake pad play is either above the maximallypermissible brake pad play or below the minimally permissible brake padplay. In the example according to FIG. 6 illustrated by the arrows, thewear at the time t=0 is above the maximally permissible brake pad play,so that the adjusting takes place as described above. As the time tincreases, that is, with a rising number of service brakings, the wearwill necessarily also increase. When the wear then again exceeds themaximally permissible brake pad play, another adjustment takes place.The described change between the wear development and the adjustingoperation will then be repeated until the brake pads 12 and the brakedisc 14 respectively have arrived at the wear limit and have to beexchanged. The case may then occur that the brake pad play is too small,so that the adjustment takes place in the opposite direction, forexample, by the inverse drive of the drive unit 10′.

A brake which has been subjected to an emergency release or an auxiliaryrelease, for example, after a brake pad exchange, is detected by anoperation of the limit switches 126′ (FIG. 2). A wear adjustingoperation takes place during each initialization of the brake at thestart of the operation after an emergency release or auxiliary releaseoperation and particularly during a test run taking place within thescope of the initialization, whose faultless pass is a prerequisite forthe subsequent operation of the brake. FIG. 7 is a program flow chart ofthe test run. First, it is determined at the branching “has auxiliaryrelease taken place” whether the brake actuator 2 is in a condition inwhich it was emergency-released or subjected to an auxiliary release,which is detected by the presence or absence of a signal of the limitswitch 126′. If it was not subjected to an auxiliary or emergencyrelease, the first program is stopped. When the brake is subjected to anauxiliary or emergency release, the brake actuator 2 is releasedaccording to the subsequent operation “release brake” by the actuatingof the servo motor 4, in order to obtain by the resulting actuation ofthe limit switch 76, a reference for the subsequent application pathmeasurement. Subsequently, as in the above-described alternativeapproach, the brake application system 1 is first actuated by theenergizing of the servo motor 4, until the brake pads 12 have reached aposition which corresponds to a defined desired application point. Thisoperation is illustrated in FIG. 7 by the operation symbol “approachapplication point in a path-controlled manner”. Subsequently, the driveunit 10′ for the wear adjusting according to the operation “switch onadjuster motor” is activated until the shearing force screw 58 detects abraking force signal for the first time, as indicated by the branching“braking force rise detected by the force sensor?”, whereby preciselythe wear path is compensated. Finally, the drive unit 10′ isdeactivated, and the brake actuator 2 is reset in the release position.

Although the present disclosure has been described and illustrated indetail, it is to be clearly understood that this is done by way ofillustration and example only and is not to be taken by way oflimitation. The scope of the present disclosure is to be limited only bythe terms of the appended claims.

1. A method of controlling an electrically actuated wear adjustingdevice of a brake application system for vehicles, particularly for railvehicles, comprising: a) determining an actual application stroke ofbrake pads from a release position to an application point onto anassigned brake disc or brake drum during a service braking having acovered application path from release to a service braking position as afunction of a measured braking force value assigned to this coveredapplication path, b) comparing the actual application stroke with adesired application or a desired-application stroke tolerance range and,if the actual application stroke deviates there from, computing anadjusting path from the deviation, and c) electronically controlling thewear adjusting device as a function of the computed adjusting path toreestablish the desired application stroke or tolerance range.
 2. Themethod according to claim 1, wherein the covered application path of thebrake pads during the service braking is measured directly or indirectlyon a moved component of the brake application system.
 3. The methodaccording to claim 2, wherein, during a service braking which took placeat a lower braking force, only the braking force value which occurredfor the first time and the assigned covered application path of thebrake pads are used for determining the actual application stroke. 4.The method according to claim 3, wherein brakings at a lower brakingforce are brakings at which braking force values occur of approximatelylower than or equal to 3% to 20% of a maximally possible braking forcevalue.
 5. The method according to claim 2, wherein, during a servicebraking which took place at a higher braking force, the braking forcevalue and the respectively assigned covered application path of thebrake pads are measured several times successively for determining abraking-force application path course, from which the actual applicationstroke is extrapolated.
 6. The method according to claim 5, whereinbrakings at a higher braking force are brakings at which braking forcevalues occur of approximately more than 3% to 20% of a maximallypossible braking force value.
 7. The method according to claim 1,wherein the wear adjuster for the wear adjusting is actuated for a timedepending on the adjusting path.
 8. The method according to claim 1,wherein the adjusting of the brake pad play takes place in the releasedor not applied condition of the brake application system.
 9. A method ofcontrolling an electrically actuated wear adjusting device of a brakeapplication system for vehicles, particularly for rail vehicles,comprising: a) operating the brake application system until the brakepads have reached a defined desired application point or a desiredapplication point tolerance range, b) electrically actuating the wearadjusting device until a measured electric braking force signal ispresent for the first time, and c) restoring the brake applicationsystem to a release position from the position the of step b.
 10. Themethod according to claim 9, wherein it is implemented at least for theupgrading or initialization from a position of the brake applicationsystem subjected to an emergency release or an auxiliary release,together with a test run.
 11. A device for controlling an electricallyactuated wear adjusting device of a brake application system forvehicles, particularly for rail vehicles, comprising: a) sensors formeasuring at least an application path from a release position to aservice braking application position covered by brake pads and a brakingforce value assigned to this application path during a service brakingand for generating corresponding output signals, b) means fordetermining an actual application stroke from the release position to anapplication point of the brake pads to an assigned brake disc or brakedrum as a function of the output signals, c) means for comparing theactual application stroke with a desired application stroke or a desiredapplication stroke tolerance range and for calculating an adjusting pathfrom the deviation, and d) means for controlling the wear adjustingdevice as a function of the calculated adjusting path to reestablish thedesired application stroke or tolerance range.
 12. The device accordingto claim 11, wherein the sensors include sensors for the path or anglemeasurement and sensors for the force measurement.
 13. The deviceaccording to claim 12, wherein the brake application system comprises aforce converter for converting energy supplied by a brake actuator to abrake application movement, and the force converter contains a shearingforce measuring screw arranged in the flow of force as the sensor formeasuring the force.
 14. The device according to claim 13, wherein theshearing force measuring screw forms a hinge pin of a hinge mutuallyconnecting at least two force transmission elements of the forceconverter, at least one strain gauge being held at the circumference ofthe shearing force measuring screw, which strain gauge generates acorresponding signal acting upon the hinge and being proportional to thejust existing braking force.
 15. The device according to claim 14,wherein the sensors for the path or angle measurement contain an angleencoder which measures the angle of rotation of a motor driving thebrake actuator and modulates a corresponding signal.
 16. The deviceaccording to claim 1, wherein the means for determining an actualapplication stroke, the means for comparing the actual applicationstroke with a desired application stroke or a desired application stroketolerance range as well as the means for controlling the wear adjustingdevice are formed by an electronic control and automatic control unithaving at least one microcomputer which communicates with the sensorsand the wear adjuster.
 17. The device according to claim 16, wherein theelectrically actuated wear adjusting device has a wear adjusterconstructed as a brake actuator, with a screw drive having a threadedspindle as a screw parts and a nut which can be screwed to the threadedspindle, one screw part of the screw drive being electrically driven forthe wear adjusting, and the other screw part being electrically drivenfor the emergency and/or auxiliary release of the brake.
 18. A vehiclebrake, particularly a rail vehicle brake, having an electricallyactuated wear adjusting device of a brake application system, containinga device according to claim
 11. 19. A method of controlling anelectrically actuated wear adjusting device of a brake applicationsystem for vehicles, particularly for rail vehicles comprising: a)determining an actual application stroke of brake pads from a releaseposition to an application point onto an assigned brake disc or brakedrum during a service braking having a covered application path fromrelease to a service braking position as a function of at least onemeasured application path traveled by the brake pads and a measuredbraking force value assigned to this covered application path, b)comparing the actual application stroke with a desired application or adesired-application stroke tolerance range and, if the actualapplication stroke deviates there from, computing an adjusting path fromthe deviation, and c) electronically controlling the wear adjustingdevice as a function of the computed adjusting path to reestablish thedesired application stroke or tolerance range, and wherein, during aservice braking which took place at a lower braking force, only thebraking force value which occurred for the first time and the assignedcovered application path of the brake pads are used for determining theactual application stroke.
 20. A method of controlling an electricallyactuated wear adjusting device of a brake application system forvehicles, particularly for rail vehicles, comprising: a) determining anactual application stroke of brake pads from a release position to anapplication point onto an assigned brake disc or brake drum during aservice braking having a covered application path from release to aservice braking position as a function of at least one measuredapplication path traveled by the brake pads and a measured braking forcevalue assigned to this covered application path, b) comparing the actualapplication stroke with a desired application or a desired-applicationstroke tolerance range and, if the actual application stroke deviatesthere from, computing an adjusting path from the deviation, and c)electronically controlling the wear adjusting device as a function ofthe computed adjusting path to reestablish the desired applicationstroke or tolerance range, and wherein, during a service braking whichtook place at a higher braking force, the braking force value and therespectively assigned covered application path of the brake pads aremeasured several times successively for determining a braking-forceapplication path course, from which the actual application stroke isextrapolated.